Learning Forum

[Brennan Donovan]

I'm trying to build a simulation for a room with ventilation. I have a couple pictures attached below. The model was made in SolidWorks and seems clean enough, I've been trying to use the SpaceClaim "fill" function to model a solid for the air in the room with no success. I've assumed it's because of the fact that the vents stretch across the room preventing the fill function from executing properly but I'm unsure. To circumvent this, I modeled extra bodies in the CAD software but when it came to meshing, the mesh failed due to too much memory being needed (the model has a lot of extra extrusions to accommodate all the space; a lot of failure points could be responsible) 

 

On a side note, this particular room, even when ran without any air modeling, has a really unstable mesh. Any meshing practices that would be recommended for a model like this would be greatly appreciated.

Model itself w/o any extra extrusions:

Mesh: 

[Rob]

The model doesn't look that complex but you're meshing the solids, and don't have a fluid region. The volume extract tools don't like voids, have you tried creating the room volume and then splitting out the air inlet/outlet parts? 

If you built the model in Solidworks why not do the volume extraction there? Then the only operation needed in SpaceClaim is boundary labelling prior to meshing. 

[Brennan Donovan]

I don't think I entirely understand but I appreciate your help. I've currently taken the model into Inventor and I'm going to try and use their volume extract tools. I did try SolidWorks' "intersect" feature to try and create the volume but it consistently failed. I believe I was operating it properly so I'll see if I can get it working in Inventor. 

 

I haven't been doing any boundary labeling in SpaceClaim prior to meshing. Once the model is approved in SpaceClaim, I have been moving to meshing. Could that be why my mesh has such high variability? What's the best way to boundary label?

I apologize if it seems like I'm skipping basic steps, I'm still learning this software and I appreciate your response.  

[Rob]

Meshing just takes the model and adds a mesh based on some pre-set criterion and anything you alter. For CFD you're looking at skew and aspect ratio, ortho quality in poly cells but you don't have those in Ansys Meshing. I'd be making IT update to 2023R2. 

Labels are useful for when you get to Fluent as they also define which surfaces are picked when you set boundary conditions. 

I think you may want to click on Help in the software and do a few tutorials. Learning (upper left on here) will also take you to a few courses that'll help. 

 

[Brennan Donovan]

I've done quite a few tutorials and always use "named selections" in Meshing to make it easier to get my boundary conditions in Fluent. However, I wasn't aware I could also do that in SpaceClaim. 

 

I've been able to get a successful simulation using the model above (successful in that all boundary conditions are defined, thermal conditions enabled with realistic outputs) but I've been struggling with this particular part of the project for awhile. I've looked at the ANSYS tutorials and haven't found any regarding a closed object when it comes to fluent. Mainly objects with fluid passing through them, not necessarily being moved in and out through parts not connected to the external world. I'll look through it again to see if I may have missed something. I haven't been able to find a tutorial on the volume extract tools either that involve creating a void where it must encapsulate separate bodies either. 

 

Do you have any tips on those two problems? I'll go through ANSYS tutorials in the meantime. Thank you. 

[Rob]

I find it's easier to create the main fluid volume and then subtract bits to form the voids afterwards. Don't just rely on the tools doing everything in one step. If you hide volumes in SpaceClaim geometry operations don't effect them, and you can then use those volumes when you unhide them. 

Named Selections in SpaceClaim are useful for going into Fluent Meshing. Otherwise, use the tools in Ansys Meshing. But, you do need the room volume before switching to meshing. I'd also lose the "thick" walls unless you REALLY want them. If they're for thermal reasons read the thin wall options in Fluent: I've never included walls in Fluent HVAC models as anything other than thin surfaces. 

[Brennan Donovan]

I had no idea about the walls and while they are there for thermal reasons, I'll first try to get them functioning as thin surfaces. 

To clarify, I should try building a new model from the fluid volume first, using a subtractive method to allocate space for the solids, "unhiding" or building the solids into the fluid volume, and using thin surfaces to contain the model? Once that's complete, use named selections in SpaceClaim (or Mesh) and ensure that all solids are accounted for before moving to meshing?

 

Thank you so much for you help, I just want to make sure I have this correct. 

 

[Rob]

Pretty much. If you create the "simple" fluid region then do the various subtraction parts you'll be sorted. If you then suppress/delete the current "wall" volume you then label the now outer faces as wall in SpaceClaim (for Fluent Meshing) or in Ansys Meshing if you take that route. 

If you search for HVAC on ansys.com you'll find a few articles that show models and will give you an idea of what we'd typically include in a simulation.